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Comment by koolba | Hacker News Reader

> The cylindrical piece of space junk is made of a metallic alloy called Inconel, they added. It weighs 1.6 pounds (0.7 kg) and measures 4 inches (10 centimeters) high by 1.6 inches (4 cm) wide.

I’m no rocket scientist, but I’m pretty sure that would kill you if you got hit. Though we’ll have to run a couple more tests to be sure.

Home owner says it tore through two floors: https://twitter.com/Alejandro0tero/status/176872903149342722...

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"One of the items I ordered was Inconel-X, I received a 3-inch diameter cylindrical billet of the material and took it to the machine shop to have a 3-inch piece cut off to make a bearing. The shop foreman fired up a band saw and started to cut the billet. He only managed to make a small groove in the billet before the cutting action stopped. The Inconel-X had destroyed the saw teeth in just a few seconds. The foreman then tried a large power hacksaw. Those saw teeth also disappeared. I then foolishly suggested he try cutting a chunk off with a cutting torch. He fired up his cutting torch and within a couple minutes we had a billet of metal that looked like taffy."

At the Edge of Space: the X-15 Flight Program

Edge Precision on Youtube posted some videos showing making a valve body out of Inconel. It's clearly a PITA, he indexes the insert (changes the cutting edge to a new one) for every single cut. That adds a lot of time, and a decent amount of expense (carbide cutting tool inserts are cheap, but not free).

This is what black boxes should be constructed with.

If you look at the Wikipedia for Inconel, it does actually mention that it is used as the engraving medium for black boxes: https://en.wikipedia.org/wiki/Inconel

Saving you guys a quick googling.

https://en.wikipedia.org/wiki/Inconel

Fascinating stuff.

Inconel is used in chemical plants for its extreme resistance to harsh chemicals which quickly corrode even the highest-quality stainless steels. Inconel (and its cousin, Monel) is primarily made from nickel (>70% for Inconel-X, >63% for monel). Stainless steel also incorporates about 10% nickel and 20% chromium. Nickel is very expensive, so if you can get away with using something with less nickel, you'd really prefer to! There are "recent" advances in corrosion-resistant steel with smaller amounts of nickel, like "duplex steel" - duplex 2204 is just slightly less corrosion resistant than 316 stainless, but contains 4% nickel instead of 10%.

You only use inconel when you absolutely cannot use anything less. It costs $2.50/lb compared to $0.80 for 316 and $0.40/lb for mild steel (standard run-of-the-mill steel). Not sure what 2204 costs these days, but will be somewhere between 316 and mild steel. No one wants to pay three times more for material if they don't have to, and also pay extra for specialized machinists who are confident working with a somewhat rare material.

Materials scientists are working hard to create new, cheaper alloys with high corrosion resistance, and it drives a lot of really cool new science! Over the past 1-4 years I've seen some super interesting articles here on HN about new science being discovered around this, but I can't find them at the moment.

That said, Inconel is only 4% denser than run-of-the-mill steel, so it's not going to make a difference which of these alloys fall from space onto your house or head.

I think it will make difference which alloy falls from space, because much more of the inconel will be left after the fall. After all, they use it in spacecraft because of how well it handles high temperatures like reentry.

It handles better high temperatures than steel in the sense that it retains its strength at high temperatures, but which are still much lower than its melting point.

This does not imply that Inconel is more resistant at vaporisation than steel. It is possible and even probable that it is less resistant (Inconel X has less chromium than many stainless steels and pure nickel has higher vapor pressure than pure iron, so it evaporates more quickly, but the behavior of alloys may be different from their components).

Therefore it is not certain that more of the inconel will be left after the fall, it is quite likely that less will be left than from stainless steels with high chromium content.

Interesting, I had assumed breakup happened because of structural failures related to aerodynamic pressure and weakened material properties as the material approaches melting. But of course vaporization would account for most of the “burning up” during reentry

Also used in oil/gas downhole in corrosive environments (primarily CO2/H2S). Typical tubing size is 2-7/8", which is ~10.4 lb/ft x thousands of feet. Not cheap.

https://super-metals.com/news/inconel-alloy-718-and-725-in-o...

Oh my gosh. I did some downhole work analyzing the corrosion of casing and tubing. It boggles my mind that some wells produce enough to justify that. I should have known - it's "only" 5-10x more in material cost; just belies my typical rule-of-thumb intuition.

You would have to have some pretty bad luck to be hit by space junk like that. Not saying it's a good thing or anything, just that the odds are pretty astronomical.

Good point. The chances are truly out of this world.

Yet possible as proven here. Hitting a home is bad enough.

The chances will probably increase the more space debris is handled in this way.

Also, tell the family they just have “bad luck”.

They're making space puns

Homes are much larger than people and people are always in their homes. And even if you were home it’s not like it would 100% penetrate a floor you’re on or wall or whatever.

The linked Twitter post above contains at least one picture of a fully penetrated floor.

US houses are notoriously not as well built as in other places in the world. Where I live at the moment for instance is concrete all around, including the roof. I would be surprised if this falling on it would do anything at all and surely wouldn’t penetrate.

Are you sure about that? It's not literally Rods From the Gods but it's a high density high heat resistance metal chunk, going very fast.

I’m not certain, no. But I’d be curious to see. In my building, each floor is around 20–30 cm thick concrete.

If a barrier can stop a .50 cal BMG, then it should be sufficient to stop space debris. 20-30 cm of concrete should be enough.

I have no idea how fast it was going when it hit, but as it is more than 10x the mass of a 50 cal, I wouldn't rely on the assumption that protection from the latter is also protection from the former.

>US houses are notoriously not as well built as in other places in the world.

I bet you could count on one hand the number of places in the world that, on average, have higher building standards than the US.

>Where I live at the moment for instance is concrete all around, including the roof.

Is the ability to stop space junk your measure here? Are we building homes or bunkers?

Where I live, the common construction for houses is to have reinforced concrete slabs as the floors and ceilings, with the walls being brick except for the load-bearing reinforced concrete columns. The ceramic tiled roof (when there's one) goes above the reinforced concrete ceiling. More than once, I've read about accidents in which Brazilians fell (sometimes to their death) through the ceiling of a USA home, and that's because we simply don't expect the ceiling to be so fragile; our intuition is that the ceiling is as strong as the floor, and that we can walk normally over it.

To those from countries with a similar building culture, USA houses feel really fragile; for instance, what do you mean you can punch a hole in a room's internal wall? We expect these walls to be made of brick.

Sure, but that concrete would break up in case of earthquake and kill a lot of people with debris. US houses are much safer in case of earthquake which is much more likely than space debris.

There are places in the US that that type of build is the norm.

Beyond that, “better built” in what sense? I’ve lived in the places that are built like bunkers (literally; Guam builds for direct typhoon hits). They are fine, but aren’t built for earthquakes, energy efficiency, or any other metric that’s more relevant in other parts of the world.

> Also, tell the family they just have “bad luck”.

It's not wrong, though.

The Earth's surface is slightly over 500 million km².

Let's say that something landing within a 10m radius of you represents a hit. That radius is about 314 m², or 0,000314 km²

If my math doesn't fail me, if we partition the globe into discrete areas equivalent to that 10m radius, the odds of something landing on your area would be around 1 in 10^12.

That's the chance of one specific person being hit. But I think you'd want to calculate the chance of any one person being "hit", which is roughly ten billion times higher than that, and uncomfortably likely (if people were actually 10m wide).

>(if people were actually 10m wide).

Apparently, we're working on that.

doesnt the orbit shadow vastly reduce surface area to a few thin overlapping strips?

Whose orbit?

the orbit/trajectory of the vessel the junk originally stemmed from

Except that neither human nor satellite distribution is even across the global surface, and we actually tend to put our satellites above the human-populated areas so that they can service those humans.

Including the nigh-unpopulated polar regions would massively skew the probabilities, for instance, especially since most satellites aren't in polar orbits either. It's still an infinitesimally small likelihood of being hit by one, of course.

> The chances will probably increase the more space debris is handled in this way.

The more stuff falls the more the models will be fine tuned to figure out how to re-enter stuff to completely burn it.

According to Clark R. Chapman (2007) [1], the "Odds of Dying in the U.S. from Selected Causes in a Human Lifetime" have Regional Asteroid/Comet Impact as 1 in 1,600,000, while the Odds of winning the PowerBall are 1 in 195,249,054.

[1] https://www2.tulane.edu/~sanelson/Natural_Disasters/impacts....

I think the odds of dying from asteroid impact come from global collapse of agriculture, not the thing falling near you.

Most asteroids aren't the Earth ending kind.

> Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles.

https://www.nasa.gov/solar-system/asteroids/asteroid-fast-fa...

Yes, but an asteroid doesn't have to be earth-ending to ruin agriculture for a year. This is similar to the civilizational threat of volcanic supereruptions.

> Good point. The chances are truly out of this world.

all the chances that are out of this world are chances of not being hit.

problem is, fully all the chances of being hit are on this world.

"if it wasn't for bad luck, I wouldn't have no luck at all." - Cousin Joe

The odds are pretty terrestrial at that point.

What's the smallest meteorite that would still be "penetrative" to a human body? Eg not falling space dust and also taking into account terminal velocities of smaller particles.

People have been hit by meteorites (which of course are more plentiful currently):

https://www.smithsonianmag.com/smart-news/only-person-ever-h...

Fixed your link: https://www.smithsonianmag.com/smart-news/only-person-ever-h...

Also, FWIW, that article says only a single person has ever been recorded as being hit by a meteorite.

The more junk the higher the probabilities of an accident. It doesn't have to reach two digits probability for it to start to be a problem. Densely populated areas + high likelihood of space debris could lead to unacceptable risks. Although I agree the actual danger is in the orbits and with deployed satellites.

Most junk burns up in the atmosphere and so is harmless. Large or dense things are a big problem though. Satellites need to be designed with respect to how they break up on reentry.

Densely populated areas probably reduce the risk for objects this size, as skyscrapers and subways are harder to go through vertically (when starting from space) than bungalows and cars.

There are 8 billions people on Earth though.

The earth surface area that is human is ~0.000000012% if you're wondering about the likelihood of being hit.

It's even lower. Need to account for time. Not every second there's space debris reaching Earth surface.

two floors huh, and then I looked at pictures...plywood home, heh in Europe it would stay on attic, no chance to penetrate 15cm of concrete and steel.

you are living in an ex-ww2 bunker? here in the UK it would have gone right through the roof tiles and the plasterboard of the ceiling. same for the several dutch houses i've lived in.

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